Drill shaft

ABSTRACT

A drill shaft capable of reducing the noise produced by percussion type rotary drilling machines is provided. The drill shaft has a housing means of conventional construction. A hollow form means, or pipe, is positioned within the housing means and extends substantially the entire length thereof. A damping means, disposed between the housing means and the hollow form means, contacts a substantial portion of the housing means and dissipates the mechanical vibrational energy imparted thereto by the striking action of a piston reciprocally moving thereabove. Once dissipated, the mechanical vibrational energy cannot be radiated in the form of air-borne noise, and the need for more expensive apparatus capable of absorbing and isolating air-borne noise is eliminated. As a result, the noise produced during operation of percussion type rotary drilling apparatus can be substantially reduced in an economical manner.

United States Patent [191 Nittinger et al.

[ June25, 1974 1 DRILL SHAFT of NJ.

[73] Assignee: Allied Chemical Corporation, New

York, NY.

[22] Filed: June 7, 1972 [21] Appl. No.: 260,649

Primary Examiner-M. Henson Wood, .lr.

Assistant Examiner-Robert Saifer Attorney, Agent, or FirmGerard P. Rooney; Ernest D. Buff 5 7] ABSTRACT A drill shaft capable of reducing the noise produced by percussion type rotary drilling machines is provided. The drill shaft has a housing means of conventional construction. A hollow form means, or pipe, is positioned within the housing means and extends substantially the entire length thereof. A damping means, disposed between the housing means and the hollow form means, contacts a substantial portion of the housing means and dissipates the mechanical vibrational energy imparted thereto by the striking action of a piston reciprocally moving thereabove. Once dis sipated, the mechanical vibrational energy cannot be radiated in the form of air-borne noise, and the need for more expensive apparatus capable of absorbing and isolating air-borne noise is eliminated. As a result, the noise produced during operation of percussion type rotary drilling apparatus can be substantially reduced in an economical manner.

9 Claims, 2 Drawing Figures 1 DRILL SHAFT BACKGROUND OF INVENTION 1. Field of the Invention This invention relates to the drilling of blast holes, wells and the like by rotary drilling methods, and more particularly to an improved drill shaft capable of reducing noise produced during the drilling operation.

2. Description of the Prior Art The rotary drilling machines which have heretofore enjoyed perhaps the widest use in mining and quarry operations are of the percussion type. In such machines, the upper end of a hollow drill shaft is repeatedly struck by a piston reciprocally moving within a cylinder thereabove. A drill bit connected to the lower end of the drill shaft is angularly displaced after each blow of the piston by a ratchet and pawl mechanism or the like. Compressed air passes in a stream down through the hollow drill shaft, across the face of the drill bit and upward through the annular space between the drill shaft and the walls of the borehole. The air stream serves to cool the drill bit and to carry drilling cuttings up the bore-hole to a dust collector at the surface of the ground.

One of the problems associated with percussion type rotary drilling machines is the difiiculty of reducing the noise produced during the drilling operation. Due to the high resonance factor of the drill shaft, thestriking action of the reciprocally moving piston produces a ringing noise which, under normal operations, often reaches a level as high as 115 decibels (dbA) or more. This level of noise interferes with the drill operators ability to converse and can gradually impair his hearing. Moreover, such noise is annoying to nearby housing residents. As a result, zoning ordinances have been enacted which impose stringent regulations governing the amount of noise emanating from drilling operations.

It has been proposed to solve the aforementioned noise problem by orienting the drill so that its quiet radiation direction points toward the nearest residential structure. This orientation of the drill is frequently prevented by requirements of the work operations. Moreover, the reduction in drill noise afforded by such orientation of the drill is minimal and, for this reason, has been generally insufficient to meet zoning ordinances. It has also been proposed to erect an enclosure around the drill to absorb and isolate the noise and thereby shadow nearby residents therefrom. Considerable costs are incurred, however, in engineering such enclosures for cooling, access and mobility. Due to the minimal reduction in drill noise practically afforded by orientation of the drill and the relatively high cost of enclosing the drill within a sound reducing structure, drilling machines of the type described have generally been operated at a noise level higher than is considered acceptable.

SUMMARY OF THE INVENTION The present invention provides an economical drill shaft capable of reducing the noise produced during the drilling operation. Such drill shaft has a housing means of conventional construction. A hollow form means, such as a pipe, is positioned within the housing means and extends substantially the entire length thereof. As used in this paragraph and whenever used hereinafter in the specification and claims, the term substantially the entire length is intended to include, as well, the entire length. The internal surface of the hollow form means provides a conduit for the passage of compressed air usedin the drilling operation. A damping means is disposed in the space between the housing means and the hollow form means. The damping means contacts a substantial portion of the housing means and reduces the vibrational energy thereof.

It has been found that contacting a substantial portion of the housing means with the damping means in the manner described above dissipates mechanical vibrational energy imparted thereto by the piston of the drilling machine. The hollow form means shields the damping means from the compressed air stream and maintains continuous contact between the damping means and the housing means. Due to the presence of such contact, the noise produced by the striking action of the piston against the drill shaft is reduced to a level far below that expected for material having such a high resonance factor.

Once the mechanical vibrational energy is dissipated by the damping means, it cannot be radiated in the form of air-borne noise. The energy need not be isolated resiliently from other radiating surfaces of the drill shaft and the need for more: expensive apparatus capable of absorbing and isolating air-borne noise is eliminated. As a result, the noise produced during operation of percussion type rotary drilling machines can be reduced by as much as 25 dbA or more in an extremely economical manner.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be more fully understood and further advantages will become apparent when reference is made to the following detailed description and the accompanying drawings in which:

FIG. 1 is a side elevational view, partly in section, of a drill shaft incorporating the elements of the present invention.

FIG. 2 is a sectional view taken through the line 2-2 of FIG. 1..

DESCRIPTION OF THE PREFERRED EMBODIMENT The drill shafts with which the present invention can be used may be fabricated in a number of diverse sizes and configurations. As a consequence, the invention will be found to function with most varieties of such drill shafts. For illustrative purposes, the invention is described in connection with a substantially cylindrical drill shaft designed to be used with a percussion type rotary drilling machine. It will be readily appreciated that the invention can be employed with drill shafts having polygonal or other similar configurations. Accordingly, the invention is intended to encompass modifications of the perferred form of drill shaft which are capable of reducing the noise produced during drilling operations.

Referring to FIG. 1 of the drawings, the drill shaft, shown generally at 10, has a housing means I2 formed from a hardened steel alloy or the like to a substantially cylindrical configuration. A substantially cylindrical hollow form means (pipe) 16 is positioned within the housing means 12 and extends substantially the entire length thereof. The inner surface 17 of the hollow form means 16 provides a conduit 14 for the passage of compressed air used in the drilling operation. A damping means 18, disposed in the substantially annular space between the housing means 12 and the hollow form means 16, contacts a substantial portion of the housing means 12 and reduces the vibrational energy thereof.

The hollow form means 16 can comprise a light gauge steel pipe which has sufficient strength to maintain its rigidity during operation of the drill shaft 10. One end 20 of the hollow form means 16 is roll expanded and flared or otherwise formed to substantially the same configuration as end portion 22 of inner surface 24 of the housing means 12. The other end 26 of hollow form means 16 is formed to substantially the same configuration as end portion 28 of the inner surface 24 in the foregoing manner. The outside diameter a of the hollow form means generally ranges from about 30 to 80 percent, preferably about 40 to 60 percent, of the inside diameter a of the housing means 12. For example, in a conventional drill shaft having an inside diameter in the order of about 4 inches, the outside diameter of the hollow form means 16 is typically about 2 inches. Generally, the hollow form means 16 is fixedly secured to the housing means 12 by tackwelding or otherwise securing the ends 20 and 26 to the inner surface 24 at the portions 22 and 28, respectively.

The damping means 18 can be made of any durable vibration damping material which can be formed in place and which will not disintegrate upon subjection for prolonged periods to the vibrations of the housing means 12. Typical vibration damping materials suitable for use as the damping means 18 include fibrous material such as asbestos or mineral wool fibers; urethane rubbers; silicone rubbers; saw dust; wood chips; heavy greases such as grease having a base which consists of lithium or calcium soap or graphite; bituminous compounds such as asphalts or tars which do not become brittle during storage; paper or wood pulp; noncompressible fluids such as lubricating or hydraulic oils, wa ter, alcohols, including methanol, ethylene glycol or glycerine; granulated plastic materials such as granulated polypropylene, polyethylene or polyvinyl chloride; and sand. Preferably, the damping means 18 is made of a damping material which comprises asbestos fibers, silicone rubbers or urethane rubbers. Generally the damping means 18 has a vibration decay rate ranging from about 4 to 400 dbA per second. Preferably the damping means 18 has a vibration damping capacity sufficient to substantially reduce the vibrational energy of the housing means 12 within a relatively short period of time. Thus the vibration damping capacity of the vibration damping means 18 is preferably sufficient to reduce the vibrational energy of the housing means 12 by about 40 to 80 dbA per second during a time period ranging from about 0.01 to 2 seconds. The amount of the damping means 18 employed depends upon the size of the drill shaft and the impact force of the piston (not shown) employed during the percussion drilling operation. Generally, the damping means 18 should contact a substantial portion of the housing means 12, as in the order of about 30 to 100 percent, preferably at least about 85 percent, of the inner surface 24 thereof, and should have an average thickness of at least about 30 percent of the average thickness of the housing means 12.

The housing means 12 is provided with one or more tapped holes 30 which communicate with the substantially annular space formed by the inner surface 24 of the housing means 12 and the outer surface 32 of the hollow form means 16. Damping means 18 is disposed within the substantially annular space by causing the damping material to flow through the tapped holes 30 and into the substantially annular space. The substantially annular space can be filled with the damping material in several conventional ways. If the damping ma terial is of the foamable variety, the substantially annular space can be filled therewith by injecting a melted charge of foamable damping material into the substantially annular space at a pressure sufficiently high to prevent foaming and then relieving the pressure from the damping material within the substantially annular space so as to allow the foaming thereofv The various methods and types of apparatus employed to dispose the damping means 18 within the substantially annular space will be well understood by those skilled in the injection molding art.

In FIG. 2 there is illustrated a sectional view of the drill shaft 10. When disposed between the housing means 12 and the hollow form means 16, the damping means 18 preferably has a substantially annular configuration. Such annular configuration of the damping means 18 reduces the vibrational energy of the housing means 12 in a highly efficient manner and is, for this reason, preferred. Other configurations of the damping means 18, including a ring-shaped structure wherein outer and inner surfaces 34 and 36 of the damping means 18 are polygonal, or a structure wherein the ring is unclosed, such as one having either a U-shaped or an arcuate form, can also be used. The form of the damping means 18 shown in FIG. 2 is intended to be illustrative and should not be interpreted to limit the scope of the invention to the particular structure disclosed. Accordingly, the term substantially annular configuration as used in the specification and claims with reference to the damping means 18 is intended to include, as well, configurations of the type discussed in this paragraph. So long as the damping means 18 contacts a substantial portion of the housing means 12, the vibrational energy of the drill shaft 10 and hence the noise produced thereby during drilling operations can be substantially reduced.

In operation, the upper end 38 of the drill shaft 10, connected to a rotary drilling machine (not shown) in the customary manner, is repeatedly struck by a piston reciprocally moving within a cylinder thereabove. A drill bit is connected to the lower end 40 of the drill shaft 10. Compressed air passes in a stream down through the conduit 14, across the face of the drill bit and upward through an annular space between the drill shaft 10 and the walls of a bore hole. Mechanical vibrational energy imparted to the housing means 12 during the percussion drilling operation is dissipated by the damping means 18. The hollow form means 16 shields the damping means 18 from the compressed air stream and maintains continuous contact between the damping means 18 and the housing means 12. Due to the presence of such contact, the concerted periodic movement of a number of molecules of the housing means 12 is progressively transformed into random movement. The number of molecules having such random movement is sufficiently large that the concerted movement of molecules at the outer surface 42 of the housing means 12 is effectively eliminated. As a result, the magnitude of sound waves (noise) produced in the surrounding air by the latter molecules is substantially reduced.

Having thus described the invention in rather full detail, it will be understood that these details need not be strictly adhered to but that various changes and modifications may suggest themselves to one skilled in the art,-

all falling within the scope of the invention as defined by the subjoined claims.

We claim:

1. A drill shaft, adapted for use in a rotary drilling operation comprising:

a. housing means for providing rigidity to the drill shaft, said housing means having a conduit therein for passage of a compressed air stream used in the drilling operation;

b. hollow form means positioned within said housing means and extending substantially the entire length thereof, the internal surface of said hollow form means providing said conduit; and

c. damping means disposed between said housing means and said hollow form means and in contact with a substantial portion of said housing means, for reducing mechanical vibrational energy of said housing means, said hollow form means being operable to shield said damping means from said compressed air stream and to maintain said damping means in continuous contact with said housing means.

2. A drill shaft as recited in claim 1 wherein said hollow form means is fixedly secured to said housing means.

3. A drill shaft as recited in claim 2 wherein each of said housing means and said hollow form means has a substantially cylindrical configuration.

4. A drill shaft as recited in claim 2 wherein said damping means has a substantially annular configuration.

5. A drill shaft as recited in claim 4 wherein said damping means has a vibration decay rate ranging from about 40 to dbA per second.

6. A drill shaft as recited in claim 5 wherein said damping means contacts from about 30 to percent of the inner surface of said housing means.

7. A drill shaft as recited in claim 6 wherein said damping means has a damping capacity sufficient to reduce the vibrational energy of said housing means by about 40 to 80 dbA per second during a time period ranging from about 0.01 to 2 seconds.

8. A drill shaft as recited in claim 7 wherein the thickness of the damping means is at least about 30 percent of the average thickness of the housing means.

9. A drill shaft as recited in claim 1 wherein said damping means is selected from the group consisting of asbestos fibers, silicone rubbers and urethane rubbers. 

1. A drill shaft, adapted for use in a rotary drilling operation comprising: a. housing means for providing rigidity to the drill shaft, said housing means having a conduit therein for passage of a compressed air stream used in the drilling operation; b. hollow form means positioned within said housing means and extending substantially the entire length thereof, the internal surface of said hollow form means providing said conduit; and c. damping means disposed between said housing means and said hoLlow form means and in contact with a substantial portion of said housing means, for reducing mechanical vibrational energy of said housing means, said hollow form means being operable to shield said damping means from said compressed air stream and to maintain said damping means in continuous contact with said housing means.
 2. A drill shaft as recited in claim 1 wherein said hollow form means is fixedly secured to said housing means.
 3. A drill shaft as recited in claim 2 wherein each of said housing means and said hollow form means has a substantially cylindrical configuration.
 4. A drill shaft as recited in claim 2 wherein said damping means has a substantially annular configuration.
 5. A drill shaft as recited in claim 4 wherein said damping means has a vibration decay rate ranging from about 40 to 80 dbA per second.
 6. A drill shaft as recited in claim 5 wherein said damping means contacts from about 30 to 100 percent of the inner surface of said housing means.
 7. A drill shaft as recited in claim 6 wherein said damping means has a damping capacity sufficient to reduce the vibrational energy of said housing means by about 40 to 80 dbA per second during a time period ranging from about 0.01 to 2 seconds.
 8. A drill shaft as recited in claim 7 wherein the thickness of the damping means is at least about 30 percent of the average thickness of the housing means.
 9. A drill shaft as recited in claim 1 wherein said damping means is selected from the group consisting of asbestos fibers, silicone rubbers and urethane rubbers. 